Transmission Selection USDM vs. JDM

[Maximus]

I have two transmissions to select from and am having some difficulty so would like to get ya'll thoughts. For this exercise, let us assume that the cost and the history/mileage of the transmissions are the same.

JDM 4.44 5spd

USDM 3.9 5spd

Thank you for your thoughts!

[iblackwe]

4.44 final drive would make a rocket but would likely not be able to keep traction. I went with the 3.9 and seem to like the taller gears as I can make 0-60 within 2nd gear vs. 3rd.

my 2 cents

[FFRSpec72]

A few of us are running the JDM 4.44 in road racing

[Maximus]

Ok, I was a little worried that the 4.44 would be too short to really enjoy on the road course/street. I do plan AutoX as well so I was hoping I could do the 4.44 and still have relatively broad application in motorsport. I can't wait to get down to VIR in this car. Thanks!

[Maximus]

So it looks like the 3.9 is a Phase 1 transmission and from what I gather I should go with the Phase 2 JDM forester motor. Had I had this information when I made the first post I may have received different responses. TY755VB1AA is the one I'll probably go with, in fact judging from the 2.0 thread, my decision is made for me. I can't seem to find that one in the transmission 2.0 thread other than knowing it is a 8-bolt Phase 2 though. Anyone have thoughts on this transmission?

[Sgt.Gator]

So it looks like the 3.9 is a Phase 1 transmission and from what I gather I should go with the Phase 2 JDM forester motor. Had I had this information when I made the first post I may have received different responses. TY755VB1AA is the one I'll probably go with, in fact judging from the 2.0 thread, my decision is made for me. I can't seem to find that one in the transmission 2.0 thread other than knowing it is a 8-bolt Phase 2 though. Anyone have thoughts on this transmission?

It's listed in the Rallispec chart I posted in the sticky. JDM Forester Turbo 1999-2000. 4.44 See http://www.rallispec.com/downloads/Transmission%20ID%20Chart_Public.pdf

[Maximus]

Yeah, i saw the ratios there, just not sure about the strength, weaknesses, and/or fitment issues people may have come across.

[Sgt.Gator]

The newer WRX 5 speeds (2008+) are stronger than the older ones. The Legacy 5 speeds (2005+) are stronger than all the older WRX and Legacy 5 speeds. None of them are very strong if you are doing hard launches.
IMHO if you can find a newer 5 speed you will be better off than a 1999 5 speed. Then it's a matter of choosing what ratios you want for your application. The LGT 5 speeds are fairly available at a cheap price because LGT owners often swap in the 6 speed.
Many folks swear by the Moore Performance blast plates. Others say they do nothing. I've never used them, but if I build a 818R with a LGT 5 speed I'll install them. http://mooreperformanceparts.com/products/blastplates/

[SixStar]

I'm running a USDM 2003 WRX box with a 3.9FD and RA gears. 4k clutch dumps on 285mm R-comps with no issues.

Modena TBD and DSS axles for strength. You should do a comparison of the 4.44FD vs the 3.9 to see where you'll be RPM vs. Speed and decide.

Assuming OEM tires and a OEM JDM 4.44:

61891

Here's the calculator to play around with RPM, tire size, ratio, etc.

http://www.tremec.com/calculadora.php

[Canadian818]

You can use the phase 1 5mt, but you'll need the phase 2 centre diff housing. Also the Moore plates won't work with Mechie's shifter linkage, afaik.

[redfogo]

You can use the phase 1 5mt, but you'll need the phase 2 centre diff housing. Also the Moore plates won't work with Mechie's shifter linkage, afaik.

Just get a phase2 trans cheaper in the long run and less work. Phase1 will bolt up no problem. But the swap work and such to get the trans to pump oil and stuff just isn't worth the work. Moore plates wont work with Mechie's shifter you can do what I did and cut them up and grind them to fit. Mine were off brand ones that came on my 2013 WRX trans so I didn't feel bad about it.. Who knows if the work now or ever did lol. I don't plan to launch anything.

[RetroRacing]

We use a 2000 JDM STI RA, big gears, 4.44's, tops out at 165mph at 7700 rpm (redline is 8250). We use only 3-5th and the gearing is perfect, pulls out of the corner like you wouldn't believe.

[Canadian818]

We use a 2000 JDM STI RA, big gears, 4.44's, tops out at 165mph at 7700 rpm (redline is 8250). We use only 3-5th and the gearing is perfect, pulls out of the corner like you wouldn't believe.

I have the same transmission, factory LSD. Did you swap the centre differential case to a newer one? Any hard launches?

[RetroRacing]

Nope, no reason to as far as I know. The 754xxxx trans is the right one for what the 818, the 752 is the one that has the issue as far as I know. Ours did not come with an lsd, they were very rare and you are very lucky. We are not using a torsen type either, happy with the clutch type as we can tune it to our use. We have a 2 way torsen type ready to go in, but I think with slicks, it will be too much stress on shafts and such to run.

[Scargo]

I'm running a USDM 2003 WRX box with a 3.9FD and RA gears. 4k clutch dumps on 285mm R-comps with no issues...

Rallispec says (http://www.rallispec.com/gea_syn_rst1140_t.html): "How much power will this gearset handle? It is difficult to provide a straight forward answer to this question because there are many contributing factors that will influence the gearset reliability. However, we have found that it is difficult to achieve good reliability in applications over 350whp that are driven aggressively. Additionally, heavy shockloading created by hard launching and flat shifting and accentuated by harsh clutches will tend to lower the reliable torque capacity of the gearset."
I would say to those considering this gearset combo and SixStar's comment is that, your mileage may vary. As Rallispec says, there are many contributing factors.
SixStar is not saying how much torque he is generating at 4K RPM. We don't know the weight of his car, the weight over the driven wheels or the tire's diameter or pavement type or the tire temperature or the tire pressure or which R-comp tires and how many heat cycles they had. It is pointless to have your tires spin easily. You want traction and the ability to apply the torque.

Rallispec also says this about the five-speed (http://www.rallispec.com/gea_syn_rst1140_t.html): "I have heard that transmission case flex is the big problem on the 5-speed, is this true? Overall there is insufficient rigidity of the bearing supports and there is flexibility in the main shaft. When you subject the gearbox to heavy loads this overall lack of rigidity allows the gears to deflect away from each other disrupting the proper gear mesh and dramatically increasing the bending loads on the gear teeth. External case reinforcements or braces will probably make little difference because the distortions are primarily of the internal structure. The bottom line is that the transmission design was never intended to support the power outputs that people are easily achieving these days."
If you upgrade to bigger, better gears you can get by with more case flex. It's still a bad deal because you are reducing the contact area and creating high pressure points as the shafts and gears move out of alignment.

Maximus, I see you are building a coupe. I don't know what your goals are but side plates and a dog box would make it quite stout.

[SixStar]

True.

I destroyed an RA set in a 280wtq car.

My 818R makes about 350wtq at 4k, enough to destroy FFR axles with ease. 2,252 with driver, 60% over the axles, 285/30-18 BFG R1Ss (24.7" dia), new and fresh, etc etc.

It's generally accepted that anything north of 300wtq on a "glass box" is risky.

[Maximus]

Rallispec says (http://www.rallispec.com/gea_syn_rst1140_t.html): "How much power will this gearset handle? It is difficult to provide a straight forward answer to this question because there are many contributing factors that will influence the gearset reliability. However, we have found that it is difficult to achieve good reliability in applications over 350whp that are driven aggressively. Additionally, heavy shockloading created by hard launching and flat shifting and accentuated by harsh clutches will tend to lower the reliable torque capacity of the gearset."
I would say to those considering this gearset combo and SixStar's comment is that, your mileage may vary. As Rallispec says, there are many contributing factors.
SixStar is not saying how much torque he is generating at 4K RPM. We don't know the weight of his car, the weight over the driven wheels or the tire's diameter or pavement type or the tire temperature or the tire pressure or which R-comp tires and how many heat cycles they had. It is pointless to have your tires spin easily. You want traction and the ability to apply the torque.

Rallispec also says this about the five-speed (http://www.rallispec.com/gea_syn_rst1140_t.html): "I have heard that transmission case flex is the big problem on the 5-speed, is this true? Overall there is insufficient rigidity of the bearing supports and there is flexibility in the main shaft. When you subject the gearbox to heavy loads this overall lack of rigidity allows the gears to deflect away from each other disrupting the proper gear mesh and dramatically increasing the bending loads on the gear teeth. External case reinforcements or braces will probably make little difference because the distortions are primarily of the internal structure. The bottom line is that the transmission design was never intended to support the power outputs that people are easily achieving these days."
If you upgrade to bigger, better gears you can get by with more case flex. It's still a bad deal because you are reducing the contact area and creating high pressure points as the shafts and gears move out of alignment.

Maximus, I see you are building a coupe. I don't know what your goals are but side plates and a dog box would make it quite stout.

Goals for now are to run stock (200-250wtq) everything until something breaks, then just upgrade as needed. The transmission was an unbeatable deal so I jumped on it. Rolling the dice to see if it bites me later, but couldn't pass it up. I ended up with the 755VB1AA and will run it as is for now.

[Canadian818]

Nope, no reason to as far as I know. The 754xxxx trans is the right one for what the 818, the 752 is the one that has the issue as far as I know. Ours did not come with an lsd, they were very rare and you are very lucky. We are not using a torsen type either, happy with the clutch type as we can tune it to our use. We have a 2 way torsen type ready to go in, but I think with slicks, it will be too much stress on shafts and such to run.

Mine is a 754xxxx trans, but it's my understanding that phase 1 transmissions lube the gears via the centre diff, and when it's removed to convert to 2wd you will not have adequate oiling. The oiling "paths" are built into the centre diff case, so by using the phase 2 case the oil gets directly to 5th gear. At least that's my understanding.

[Maximus]

My understanding is the same for Phase 2 transmissions, which my 755 is. I can pair this with Craig's mod and a MR2 shifter, correct?